I need a controller but arent sure which one for my needs

Right, this comes up constantly so let me give you the framework rather than just an answer, because the answer depends on things you haven't told us yet.

PWM vs MPPT — the actual decision:

PWM is fine if your panel voltage closely matches your battery voltage. For a 12V system that means panels with a Vmp around 17-18V. Job done, cheap controller, move on.

MPPT makes sense when your panel Vmp is significantly higher than your battery voltage — the controller harvests that extra voltage and converts it into usable amps. On a 12V system with a modern 30V+ Vmp panel (which is basically everything sold now), you're leaving real power on the table without MPPT.

The numbers you actually need to share:

• Panel Voc and Vmp
• Panel Isc and Imp
• Number of panels and how they're wired
• Battery chemistry (lead-acid, LiFePO4, AGM, gel — they all want different charge profiles)

I run a Victron SmartSolar 100/20 on my shepherd's hut setup — overkill for some, but the Bluetooth monitoring alone is worth it to me. Fogstar lithiums need proper LiFePO4 charge curves and cheap no-name controllers can be genuinely dangerous with them.

Renogy do decent budget MPPT units if Victron pricing stings. Just avoid the absolute bargain-bin stuff from unknown brands — the protection circuitry is often nonexistent.

Post your panel specs and battery setup and I'll give you a straight answer. Others here will too.

Cheers @FormerMechanic14, solid framework. One thing I'd add that trips people up — don't forget to account for your battery bank voltage when choosing. I made the mistake early on of buying a decent MPPT unit without checking it could handle my 24V system properly, and some of the cheaper ones have quirks around voltage detection on initial startup. Also worth mentioning that if you're buying secondhand (which plenty of us do to keep costs down), Victron gear holds its value brilliantly but also tends to work reliably for years, so it's often worth the extra on the used market over a cheap new Chinese unit with dodgy specs.

Good point from @JimChapman74 — battery voltage matters more than people realise. Had a mate wire up a lovely 24V MPPT to a 12V system and wonder why his Victron SmartSolar was having an existential crisis.

Quick rule of thumb that saves headaches:

• Panel Voc must not exceed controller

Really important point from @BrianBrown that I'd reinforce from bitter experience — I wired my narrowboat's entire 48V system before realising my shortlisted Victron SmartSolar 100/30 was rated for panels up to 100V open-circuit, not 100V system voltage. Completely different thing. Read the spec sheet twice.

Also worth flagging for anyone shopping on a budget: the cheap Renogy PWM units are perfectly decent for small static setups, but the moment you're running panels in partial shade or your panel voltage is meaningfully higher than your battery bank, you're leaving real money on the table every single day. MPPT pays for itself surprisingly quickly in UK conditions where diffuse light is the norm rather than exception.

What's your panel configuration and battery voltage, @FormerMechanic14? That'll narrow it down properly.

@OffGridTel that 48V story made me wince — I've had a similar near-miss on my own narrowboat, though mine involved a Victron SmartSolar that I'd almost programmed for lithium when it was still connected to AGMs. The "almost" is doing a lot of heavy lifting in that sentence.

One thing nobody's mentioned yet: cable runs matter enormously on a boat. My panels are mounted on the cabin roof, which means I've got a decent run back to the controller. With PWM, every volt dropped in that cable is gone forever. With MPPT, the higher input voltage means proportionally lower current, which means thinner — or shorter-feeling — cable losses. On a narrowboat where you're routing through bulkheads and under gunwales, this can genuinely tip the economics in favour of MPPT even on a modest system.